Generation of domain models from noisy transcriptions

ABSTRACT

A method of building a domain specific model from transcriptions is disclosed. The method starts by applying text clustering to the transcriptions to form text clusters. The text clustering is applied at a plurality of different granularities, and groups topically similar phrases in the transcriptions. The relationship between text clusters resulting from the text clustering at different granularities is then identified to form a taxonomy. The taxonomy is augmented with topic specific information.

FIELD OF THE INVENTION

The present invention relates generally to speech processing and, in particular, to the generation of domain models from transcriptions of conversation recordings.

BACKGROUND

Call-center is a general term used in relation to help desks, information lines and customer service centers. Many companies today operate call-centers to handle a diversity of customer issues. Such may include product and services related issues and grievance redress. Call-centers are constantly trying to increase customer satisfaction and call handling efficiency by aiding agents and agent monitoring.

Call-centers may use a dialog-based support, relying on voice conversations and on line chat, and email support where a user communicates with a professional agent via email. A typical call-center agent handles over a hundred calls in a day. These calls are typically recorded. As a result, gigabytes of data are produced every day in the form of speech audio, speech transcripts, email etc. This data is valuable for doing analysis at many levels. For example, the data may be used to obtain statistics about the type of problems and issues associated with different products and services. The data may also be used to evaluate call center agents and train the agents to improve their performance.

Today's call-centers handle a wide variety of domains, such as computer sales and support, mobile phones, apparel, car rental, etc. To analyze the calls in any domain, analysts need to identify the key issues in the domain. Further, there may be variations within a domain based on the service providers. An example of a domain where variations within the domain exist that are based on the service providers is the domain of mobile phones.

In the past an analysts would generate a domain model through manual inspection of the data. Such a domain model can include a listing of the call categories, types of problems solved in each category, listing of the customer issues, typical question-answers, appropriate call opening and closing styles etc. In essence, these domain models provide a structured view of the domain.

Manually building such domain models for various domains may become prohibitively resource intensive. Many of the domain models are also dynamic in nature and therefore change over time. For example, when a new version of a mobile phone is introduced, when a new software product is launched in a country, or when a new computer virus starts an attack, the domain model may need to be refined.

In view of the foregoing, a need exists for an automated approach of creating and maintaining domain models.

SUMMARY

It is an object of the present invention to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements.

According to an aspect of the present invention there is provided a method of building a domain specific model from transcriptions. The method starts by applying text clustering to the transcriptions to form text clusters. The text clustering is applied at a plurality of different granularities, and groups topically similar phrases in the transcriptions. The relationship between text clusters resulting from the text clustering at different granularities is then identified to form a taxonomy. The taxonomy is augmented with topic specific information.

Preferably the taxonomy is augmented with one or more of: typical issues raised and solutions to those issues; typical questions and answers; and statistics relating to conversations associated with said transcriptions.

In a further preferred implementation the method starts with the initial step of extracting from the transcriptions n-grams based upon their respective frequency of occurrences.

The identifying step preferably identifies relationships between text clusters resulting from the text clustering at granularities of adjacent levels.

Other aspects of the invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described with reference to the drawings, in which:

FIG. 1 shows a schematic flow diagram of a method of building a domain specific model from a collection of telephonic conversation recordings;

FIG. 2 shows a partial transcript of a dialog from the internal IT help desk of a company;

FIG. 3 shows a part of the taxonomy obtained from the dialogs from the internal IT help desk of a company;

FIG. 4 shows a part of topic specific information that has been generated for the “default properti” node in FIG. 3 from an example case;

FIG. 5 shows average call duration and corresponding average transcription lengths for topics of interest;

FIG. 6 shows variation in prediction accuracy as a function of the fraction of a call;

FIG. 7 shows a graph of the prediction accuracy achieved for various clusters after analyzing 25%, 50%, 75% and 100% of the call; and

FIG. 8 is a schematic block diagram of a general purpose computer upon which arrangements described can be practiced.

DETAILED DESCRIPTION

FIG. 1 shows a schematic flow diagram of a method 100 of building a domain specific model 190 from a collection of conversation recordings 105, such as telephonic conversation recordings. The domain specific model 190 built by the method 100 comprises primarily a topic taxonomy, where every node in the taxonomy is characterized for example by topic(s), typical Question-Answers (QAs), typical actions call statistics etc.

The method 100 is described in the context of a call-center where a customer phones a call-center agent for assistance. However, the method 100 is not so limited. In the embodiment described the conversation recordings 105 comprise dialog between the call-center agent and the customer.

The method 100 of building a domain specific model from a collection of conversation recordings 105 may be practiced using a general-purpose computer system 800, such as that shown in FIG. 8 wherein the processes of FIG. 1 may be implemented as software, such as an application program executing within the computer system 800. In particular, the steps of the method 100 are affected by instructions in the software that are carried out by the computer system 800. The software may be stored in a computer readable medium. The software is loaded into the computer system 800 from the computer readable medium, and then executed by the computer system 800. A computer readable medium having such software or computer program recorded on it is a computer program product. The use of the computer program product in the computer system 800 preferably effects an advantageous apparatus for building a domain specific model 190 from a collection of conversation recordings 105.

The computer system 800 is formed by a computer module 801, input devices such as a keyboard 802, output devices including a display device 814. The computer module 801 typically includes at least one processor unit 805, and a memory unit 806. The module 801 also includes an number of input/output (I/O) interfaces including a video interface 807 that couples to the display device 814, and an I/O interface 813 for the keyboard 802. A storage device 809 is provided and typically includes at least a hard disk drive and a CD-ROM drive. The components 805 to 813 of the computer module 801 typically communicate via an interconnected bus 804 and in a manner which results in a conventional mode of operation of the computer system 800 known to those in the relevant art.

Typically, the application program is resident on the storage device 809 and read and controlled in its execution by the processor 805. In some instances, the application program may be supplied to the user encoded on a CD-ROM or floppy disk and read via a corresponding drive, or alternatively may be read by the user from a network via a modem device. Still further, the software can also be loaded into the computer system 800 from other computer readable media. The term “computer readable medium” as used herein refers to any storage medium that participates in providing instructions and/or data to the computer system 800 for execution and/or processing.

The method 100 may alternatively be implemented in dedicated hardware such as one or more integrated circuits performing the functions or sub functions of method 100.

Referring again to FIG. 1, the method 100 starts in step 110 where the dialog of the conversation recordings 105 is automatically transcribed to form transcription output 115. For example, in the case of telephonic conversation recordings automatic speech recognition (ASR) may be used to automatically transcribe the dialog of the conversation recordings 105.

The transcription output 115 comprises information about the recognized words along with their durations, i.e. start and end times of the words. Further, speaker turns are marked, so the speaker portions are demarcated without exactly naming which part belongs to which speaker.

However, the transcription output 115 contains many errors and a high degree of noise. The method 100 is capable of managing the errors and noise through various feature engineering techniques.

Before describing the feature engineering techniques in more detail the origin of the errors and noise is first discussed. Current ASR technology, when applied to telephone conversations, has moderate to high word error rates. This is particularly true for telephone conversations arising from call-center calls, because call-centers are now located in different parts of the world, resulting in a diversity of accents that the ASR has to contend with. This high error rate implies that many wrong deletions of actual words and wrong insertion of dictionary words are common phenomena. Also, speaker turns are often not correctly identified and portions of both speakers are assigned to a single speaker.

In addition to speech recognition errors, there are other challenges that arise from recognition of spontaneous speech. For example, there are no punctuation marks. Silence periods are marked, but it is not possible to find sentence boundaries based on these silences. There are also repeated words, false starts, many pause filling words such as “um” and “uh”, etc.

FIG. 2 shows a partial transcript of a dialog from the internal IT help desk of a company. As can be seen from the partial transcript, due to the high error rate and introduced noise, the transcription output 115 is difficult for humans to interpret.

Referring again to FIG. 1, in order to combat the noise introduced by the ASR, the method 100 continues to step 120 where various feature engineering techniques are employed to perform noise removal. More particularly, a sequence of cleansing operations are performed to remove generic stopwords such as “the”, “of”, etc., as well as domain specific stopwords such as “serial”, “seven”, “dot” etc. Pause filling words, such as “um”, “uh”, and “huh” are also removed.

The words remaining in the transcription output are passed through a stemmer. The stemmer determines a root form of a given inflected (or, sometimes, derived) word form.

For example, the root “call” is determined from the word “called”. In the preferred implementation Porter's stemmer available from http://www.tartarus.org.martin/PorterStemmer is used.

The next action performed in step 120 is that all n-grams which occur more frequently than a threshold, and do not contain any stopword, are extracted from the noisy transcriptions.

Next, in step 130, text clustering is applied to the output of step 120 to group topically similar conversations together. In the preferred implementation the clustering high dimensional datasets package (CLUTO package) available from http://glaros.dtc.umn.edu/gkhome/views/cluto is used for the text clustering, with the default repeated bisection technique and the cosine function as the similarity metric.

The transcriptions do not contain well formed sentences. Therefore, step 130 applies clustering at different levels of granularity. In the preferred implementation 5 clusters are firstly generated from the transcriptions. Next, 10 clusters from the same set of transcriptions are generated, and so on. At the finest level 100 clusters are generated.

The relationship between groups at different levels of granularity is identified by generating a taxonomy of conversation types in step 140. Step 140 firstly removes clusters containing less than a predetermined number of transcriptions, and secondly, introduces directed edges from cluster ν₁ to cluster ν₂ if clusters ν₁ and ν₂ share at least one transcription between them, where cluster ν₂ is one level finer than cluster ν₁. Clusters ν₁ and ν₂ thereby become nodes in adjacent layers in the taxonomy. Each node in the taxonomy may be termed a topic.

A top-down approach is preferred over a bottom-up approach because it indicates the link between clusters of various levels of granularity and also gives the most descriptive and discriminative set of features associated with each node (topic). Descriptive features are the set of features which contribute the most to the average similarity between transcriptions belonging to the same cluster. Similarly, discriminative features are the set of features which contribute the most to the average dissimilarity between transcriptions belonging to different clusters. These features are later used for generating topic specific information.

FIG. 3 shows a part of the taxonomy obtained from the dialogs from the internal IT help desk of a company. The labels shown in FIG. 3 are the most descriptive and discriminative features of a node given the labels of its ancestors.

Referring again to method 100 shown in FIG. 1, the taxonomy generated in step 140 is augmented in step 150 with various topic specific information related to each node, thereby creating an augmented taxonomy. The topic specific information includes phrases that describe typical actions, typical QAs and call statistics for each topic (node) in the taxonomy.

Typical actions correspond to typical issues raised by the customer, problems and strategies for solving such problems. The inventors have observed that action related phrases are mostly found around topic features. Accordingly, step 150 starts by searching and collecting all the phrases containing topic words from the documents belonging to the topic. In the preferred implementation a 10-word window is defined around the topic features, and all phrases from the documents are harvested. The set of collected phrases are then searched for n-grams with frequency above a preset threshold. For example, both the 10-grams “note in click button to set up for all stops” and “to action settings and click the button to set up” increase the support count of the 5-gram “click button to set up”.

The search for the n-grams proceeds based on a threshold on a distance function that counts the insertions necessary to match two phrases. For example, the phrase “can you” is closer to the phrase “can<:::>you” than to the phrase “can<:::><:::>you”. Longer n-grams are allowed a higher distance threshold than shorter n-grams. Next, all the phrases that frequently occur within the cluster are extracted.

Step 150 continues by performing phrase tiling and ordering. Phrase tiling constructs longer n-grams from sequences of overlapping shorter n-grams. The inventors have noted that the phrases have more meaning if they are ordered by their respective appearance. For example, if the phrase “go to the program menu” typically appears before the phrase “select options from program menu”, then it is more useful to present the phrases in the order of their appearance. The order is established based on the average turn number in the dialog where a phrase occurs.

Consider next a situation or a case of typical Question-Answers sessions in a call centre. To understand a caller's issue the call center agent needs to ask the appropriate set of questions. Asking the right questions is the key to handle calls effectively. All the questions within a topic are searched for by defining question templates. The question templates look for all phrases beginning with the terms “how”, “what”, “can I”, “can you”, “were there” etc. All 10-word phrases conforming to the question templates are collected and phrase harvesting, tiling and ordering is done on those 10-word phrases. For the answers a search is conducted for phrases in the vicinity immediately following the question.

FIG. 4 shows a part of the topic specific information that has been generated for the “default properti” node in FIG. 3 from an example case comprising 200 transcription outputs 115. 123 of the transcription outputs 115 contained the topic “default properti”. In the example case, phrases that occur at least 5 times in these 123 transcription outputs 115 were selected. The general opening and closing styles used by the call-center agents in addition to typical actions and QAs for the topic have been captured. The transcription outputs 115 associated with the “default properti” node in FIG. 3 pertain to queries on setting up a new network connection, for example from AT&T. Most of the topic specific issues that have been captured relate to the call-center agent leading the caller through the steps for setting up the network connection.

The following observations can be made from the topic specific information that has been generated:

-   -   Despite the fact that the ASR step 110 introduces a lot of         noise, the phrases captured are well formed. The resulting         phrases, when collected over the clusters, are clean.     -   Some phrases appear in multiple forms. Consider for example the         phrases, “thank you for calling how can i help you”, “how may i         help you today”, “thanks for calling can i be of help today”.         While tiling is able to merge matching phrases, semantically         similar phrases are not merged.

With regards to call statistics, various aggregate statistics for each node in the topic taxonomy are captured as part of the domain specific model namely (1) average call duration (in seconds), (2) average transcription length (number of words) (3) average number of speaker turns and (4) number of calls. Generally the call durations and number of speaker turns varies significantly from one topic to another.

FIG. 5 shows average call duration and corresponding average transcription lengths for a few topics of interest. It can be seen that in topic cluster-1, which relates to expense reimbursement and associated issues, most of the queries were answered relatively quickly when compared to topic cluster-5, for example. Cluster-5 relates to connection related issues. Calls associated with connection related issues require more information from callers and are therefore generally longer in duration. Interestingly, topic cluster-2 and topic cluster-4 have similar average call durations but substantially different average transcription lengths. Cluster-4 is primarily about printer related queries where the customer is often not ready with details, such as printer name and the Internet Protocol (IP) address of the printer, resulting in long hold times. In contrast thereto, cluster-2 which relates to online courses have a shorter transcription length because users generally have details like course name etc. ready and are interactive in nature. It should be apparent to a person skilled in the art that various other clusters may be formed and used, which fall within the scope of the present invention.

A hierarchical index of type {topic→information} based on this automatically generated domain specific model is then built for each topic in the topic taxonomy. An entry of this index contains topic specific information namely (1) typical QAs, (2) typical actions, and (3) call statistics. The information associated with each topic becomes more and more specific the further one goes down this hierarchical index.

The domain specific model may be further refined by semantically cluster topic specific information so that redundant topics are eliminated. Topics in the model may also be linked to technical manuals, catalogs etc. already available on the different topics in the given domain.

Having described the method 100 of building a domain specific model from a collection of telephonic conversation recordings 105, applications of the domain specific model is next described.

Information retrieval from spoken dialog data is an important requirement for call-centers. Call-centers constantly endeavor to improve the call handling efficiency and identify key problem areas. The described domain specific model provides a comprehensive and structured view of the domain that can be used to do both. The domain specific model encodes three levels of information about the domain, namely:

-   -   General: The taxonomy along with the labels gives a general view         of the domain. The general information can be used to monitor         trends on how the number of calls in different categories         changes over time e.g. daily, weekly, monthly.     -   Topic level: This includes a listing of the specific issues         related to the topic, typical customer questions and problems,         usual strategies for solving the problems, average call         durations, etc. The topic level of information can be used to         identify primary issues, problems and solutions pertaining to         any category.     -   Dialog level: This includes information on how agents typically         open and close calls, ask questions and guide customers, average         number of speaker turns, etc. The dialog level information can         be used to monitor whether agents are using courteous language         in their calls, whether they ask pertinent questions, etc.

The {topic→information} index requires identification of the topic for each call to make use of information available in the domain specific model. Many of the callers' complaints can be categorized into coarse as well as fine topic categories by analyzing only the initial part of the call. Exploiting this observation fast topic identification is performed using a simple technique based on distribution of topic specific descriptive and discriminative features within the initial portion of the call.

FIG. 6 shows variation in prediction accuracy using the method 100 as a function of the fraction of a call observed for 5, 10 and 25 clusters. It can be seen, at coarse level, nearly 70% prediction accuracy can be achieved by analyzing the initial 30% of the call and more than 80% of the calls can be correctly categorized by analyzing only the first half of the call.

FIG. 7 shows a graph of the prediction accuracy achieved for various clusters after analyzing 25%, 50%, 75% and 100% of the call. It can be seen that calls related to some clusters can be quickly detected compared to some other clusters.

A further application of the domain specific model is in an aiding and administrative tool. One such a tool operates by aiding call-center agents to efficient handle calls, thereby improving customer satisfaction as well as to reduce call handling time. Another is an administrative tool for agent appraisal and training.

Call-centre agent aiding is primarily driven by topic identification. As can be see from FIG. 6, in order to achieve 75% prediction accuracy, a “level-1” topic, which corresponds to the 5-cluster level, can be identified within the first 30% of the calls. Similarly, a “level-2” topic, which corresponds to a 10-cluster level, can be identified within the first 42% of the calls, and a “level-3” topic, which corresponds to a 25-cluster level, can be identified within the first 62% of the calls.

The hierarchical nature of the model assists in providing generic to specific information to the agent as the call progresses. For example, once a call has been identified as belonging to topic {lotusnot} (FIG. 3), the call-center agent is prompted with generic Lotus Notes related QAs and actions. Within the next, say, 45 seconds the tool identifies the topic to be the {copi archive replic} topic, and the typical QAs and actions in the prompts change accordingly. Finally, the tool identifies the topic as the {servercopi localcopi} topic and comes up with suggestions for solving the replication problem in Lotus Notes.

The administrative tool is primarily driven by dialog and topic level information. This post-processing tool is used for comparing completed individual calls with corresponding topics based on the distribution of QAs, actions and call statistics. Based on the topic level information it can be verified whether the agent identified the issues correctly, and offered the known solutions on a given topic. The dialog level information is used to check whether the call-center agent used courteous opening and closing sentences. Calls that deviate from the topic specific distributions are identified in this way and agents handling these calls can be offered further training on the subject matter, courtesy etc. This kind of post-processing tool may also be used to identify abnormally long calls, agents with high average call handle times etc.

The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive. 

1. A method of building a domain specific model from transcriptions, said method comprising the steps of: applying text clustering to said transcriptions to form text clusters, where said text clustering is applied at a plurality of different granularities and groups topically similar phrases in said transcriptions; identifying the relationship between text clusters resulting from said text clustering at different granularities to form a taxonomy; and augmenting said taxonomy with topic specific information.
 2. The method according to claim 1 wherein said taxonomy is augmented with one or more of: typical issues raised and solutions to those issues; typical questions and answers; and statistics relating to conversations associated with said transcriptions.
 3. The method according to claim 1 comprising the initial step of: extracting from said transcriptions n-grams based upon the respective frequencies of occurrences of the n-grams.
 4. The method according to claim 1 wherein said identifying step identifies relationships between text clusters resulting from said text clustering at granularities of adjacent levels.
 5. The method according to claim 1 comprising the initial steps of: removing stopwords from said transcriptions; and removing pause filling words from said transcriptions.
 6. The method according to claim 5 wherein said stopwords include generic stopwords and domain specific stopwords.
 7. A method comprising the steps of: receiving a domain specific model; receiving a transcription of a part of a conversation; and mapping said transcription to a node in said domain specific model.
 8. A method comprising the steps of: receiving a domain specific model; receiving a transcription of a conversation; calculating statistics of said transaction; and comparing at least said statistics of said transcription with statistics from said domain specific model.
 9. An apparatus for building a domain specific model from transcriptions, said apparatus comprising a processor configured to perform the steps comprising of: applying text clustering to said transcriptions to form text clusters, where said text clustering is applied at a plurality of different granularities and groups topically similar phrases in said transcriptions; identifying the relationship between text clusters resulting from said text clustering at different granularities to form a taxonomy; and augmenting said taxonomy with topic specific information.
 10. The apparatus according to claim 9 wherein said taxonomy is augmented with one or more of: typical issues raised and solutions to those issues; typical questions and answers; and statistics relating to conversations associated with said transcriptions.
 11. The apparatus according to claim 9 wherein said processor is configured to perform the further step of: extracting from said transcriptions n-grams based upon the respective frequencies of occurrences of the n-grams.
 12. The apparatus according to claim 9 wherein said identifying step identifies relationships between text clusters resulting from said text clustering at granularities of adjacent levels.
 13. An apparatus configured to perform the steps comprising of: receiving a domain specific model; receiving a transcription of a part of a conversation; and mapping said transcription to a node in said domain specific model.
 14. An apparatus configured to perform the steps comprising of: receiving a domain specific model; receiving a transcription of a conversation; calculating statistics of said transaction; and comparing at least said statistics of said transcription with statistics from said domain specific model. 